Part of the problem with the guys you mentioned in the first post is that nearly all of them came into the game late.

It's not like they were taught at a young age, and continuously worked on their skills while growing.

I think that's one of the big things here.

Promoters see them and think, that's a big dude, he could probably fight or be an attraction, most of those guys started boxing after they grew.

This is true. The training they also received is rather suspect. Tye Fields literally can't fight in all seriousness, and any fight he has won is due to his great size and work ethic. The Klitschko brothers received training in combat sports since a very young age and are obviously very gifted athletes as well.